Method of making steel piston rings



Nov. 25,-..1930. L. c. MARSHALL 83,047

METHOD OF MAKING STEEL PISTON RINGS Filed June 1, 1927 2 Sheets-Sheet 1 [at lewis amamskaa b a Q Nov. 25, 1930. c. MARSHALL 1,733,047

METHOD OF MAKING STEEL PISTON RINGS Filed June 1. 192' 2 Sheets-Sheet 2 t M m 26 f R a/ Mk9 a5 .2

I Patented] Nov. 25,-

PATENT orFlcE :cEwIs c. MARSHALL, or wenronnrmssnonnsnrrs METHOD OI MAKINGSTEEL PISTON RINGS Application filed me '1, 1927. "serial no. 195,720.

' This invention pertains to piston ringsfor internal combustion engines and the like and I more particularly to; a method of making such rings from hard steel wire or rod. In my copending application Serial,No.. 62,825, filed-v O ctober 10, 1925, I have described my discovery that piston rings of hard steel or steel alloy having physical characteristics similar to that of steel ofat least 0.5% carbon (or peferably steel of approximately0.65% car v bon) form a good'working surface in contact with the cylinder wall and exhibit no tendency to score the cylinder wall. In said application I have also described one desirable process-of producing suchrings and apparatus useful in performing such process. In

my copending application-Serial No. 195,719

filed June 1, 1927, I have disclosed and claimed more specifically certain desirable steps in the production of such rings together with appropriate means for performing those particular .steps. k

The present. invention relates to a modified and improved methodembodying certain of the process steps set forth in my above-named applications as well as others not. therein specifically disclosed and has been perfected in the endeavor to simplify'and cheapen the production of piston rings on a commercial scale. While the specific order of steps hereinafter described is desirable and results in the production of commercially acceptable rings, I do not limit myself to this specific series of steps nor to the inclusion'of all of the steps herein described or their equivalents and I contemplatethe substitutionjand addi- 1 tion ofother steps as falling within the.

province of my broad invention.

- In the accompanying drawings I have illustrated most of the several steps (herein described as constituting the complete process) b reference to rings or portions of rings sli owing the results of such steps and in some instances I have illustrated appliances useful above noted, to disclose such instruments or .sirable I in performing one or more of such steps, but

machines in detail .in the drawings.

In the drawings, 7 Fig. 1 is a fragmentary enlarged perspective 'view illustrating a piece of wire or rod 5 accompanying rings; I

Fig. 2 is a transverse section, to larger scale, showingthe wireor rod of Fig. 1 and indicating the shape whichthis wire assumes afterbending;

Fig. 3 is a view illustrating intransverse section various shapes of wire which might conceivably be employed in making piston rings in accordance with thi-smethod;

Fig. is a plan view showing a section oi of a preferred shape useful in making piston .the wire bent to form a single annular turn having a gap therein;

Fig. 5 is aview illustrating results some times [produced by the bending process and in forming the gap in the ring;

Fig. 6 is a; fragmentary elevation illustrating the step of removing'the burr from the ends of the ring; I

"Figs. 7 and 8 are a transverse section and a fragmentary perspective view, respectively,

illustrating vshapes which sometimes result from the bending operation;

. Fig. 9 is afragmentary side elevation, partly in section, illustrating a method of fla-tteningthe radial faces of the ring and conforming it to the axial thickness desired;

Fig. 10 is a transverse section illustrating the results of the operation of Fig. 9;

Fig. 11 is a side elevation showing a ring after the operation of Fig. 9 and indicating a characteristic of the ring which is frequently present but which is not always de- Figs. 12, 13 and 14 are views illustrating a device useful in heat treating the ring to reduce it to fiat or plane form;

Fig. 15 is a fragmentary elevation show ing' aseries of rings mounted upon the deviceof Figs. 12, 13 andl; y

Fig. 16 is a horizontal section substantially on the line 1'6- 16 of Fig. 15, showing rings'mounted in position for heat treatment; v Fig. 17 is an elevation illustrating one.

- means fortrimmin the ends of the r-ing and producing Y the deslredv width and shape of Fig. 18 is a fragmentary side elevation of the mug showing the gap formed by the'operation of Fig. 17;

Fig. 19 is-a fragmentary plan view of the shown in Fig. 18; ig. 20 is a view similar to Fig. 18' but showlng a modified construction for the end of the ring;

- high temperature, met with. in internal Fig. 21 is a side elevation illustrating the. operation of .removing burrs formed in cut ting the gap;

Fig. 22' is a side elevation illustrating the operation of flattening the radiaT faces of the ring by grinding;

Fig. 23 1s a similar view illustrating the process of flattening of the radial faces by impact or compression;

Fig. 24 is a side elevation of a mandrel composition which by test has been proven to form agood working surface in contact with the wall of an engine cylinder, that is to say, the material chosen should be such that it does not score the cylinder wall when moved rapidly in contact therewith at the combustion engine practice and which is capable of expanding resiliently against the linder walls to produce the desired gas tight fit. This material must also be of a character sucll that it is capable of underoing the various steps of the process as eremafter described, one essential characteristic beingthat it shall be ductile or capable of bendingwithout danger of breaking,

in other words this material must be toughand not brittle.

As pointed out in my aforesaid. pending application Serial No. 62,825, attempts have been. made in the past'to make piston rings from ductile material, such for example as mild steel or copper, by a process involving metals, and I am unaware that any one prior bending or similar operations, but heretofore so far as is known to me such efforts have been;confined to the employment of the mild or low carbon steels or other soft to my discovery has ever recognized the fact thatahard steel, that is to say, steel of at 0.5% carbon, makes a perfect wearing fit against a cylinder wallwithout I scoring or biting into the cylinder wall.

of steel of a carbon content of 0.5% carbon I have experimented with various grades I or more and as a result of my experiments I am led to believe that any steel of a carbon content above ..that noted exhibits these de sirable characteristics, although I findv that' steel of appfrximately'0.65% carbon is particularlysatisfactory since, while it produces a very good wearing surface, it is not so extremely hard as torender its working unduly diflicult. I have also experimented with certain alloy steels and .in consequence of these experiments believe that any steel having the general physical characteristics (particularly the hardness) of steel of 0.5% car- I bon or of a carbon content greater than that will give satisfactory results.

Having selected a material exhibiting the physical characteristics above noted, Ihave this material formed into rod or wire, and if the piston ring to be produced is to have'a substantially rectangular cross section, I refer to employ wire 1 such as is shown in ig; 2,.that is, wire of substantially trapezoidal section having the wide face 2 and the relatively narrow face 3. In the drawings the difference in width of these faces is very greatly exaggerated for illustrative purposes,

. but in actual practice this difli'erence may be of'the order of 0.005 inches. When wireof this section is bent with its narrow face 3 at I y the inside of the arc, I find that during bending the metal flows to such an extent'that the wire assumes a substantiall cross section as indicated in Fig. 2. I

While this particular shape of wire is desirable for the reasons noted, I contemplate that for very special purposes wire of other otted lines in I section may be employed, and in Fig. 3 I have indicated at 4, 5, 6 7, 8 and 9 certain sha of wire which might be found useful, un er some circumstances, it being noted that the shapes here shown are not to be taken as comprehensive of all possible shapes, but that wire ofany desired shape might be employed rforming the presentprocess. Havmg thus selected the materiaI andthe shape of wire to be employed Ibe'nd-this wire in any desired manner by the use, if desired, of any suitable instruments or mechanism, such for example as is disclosed in my copending aprplication Serial No. 195,719, filed June 1, 192 to form a single annular turn 10 as indicated in Fig. 4. Whilethis annular turn may be.

'substantiallycircular as formed, I prefer to make it of slightly elliptical shape with the long axis indicated at 11' and the short axis rectangular at 12,'and at one end of the shorter axis 12 I provide a gap 13. This gap-maybe formed concomitantly with the bending rocess and if desired in severing the turn formed by bending) from the original length of wire. Thus as disclosed in my copendlng application just'referredto, one desirable mode of bending the wire to form the rough or unfinished ring comprises advancing a length of wire or rod while confining it between ap-' propriate bending devices or implements which constrain the advancin' wire to assume an arcuate curvature. Pre era'bly the advance of the wire'is intermittent, andduring each advance to form a single annular turn the bending devices or implements are relatively moved so as to vary the radius of curvature of the bending wire, thereby producing a ring of flattened or-elliptical shape adapted to expand uniformly when the ring is placed in an engine cylinder. As the wire is advanced, it is guided in a helical path, the pitch of which is so moderate that the limit of elasticity of the wire is not exceeded. When one turn has been completed, the advance of the wire is preferably stopped and the turn is cut off b a radial or diagonal cut,

as may be preferre and at such apoint that the severed turn is slightly less than a com-- durin the advance. of the wire may be dispense with so that the rough or embryo rin will be of circular rather than of elliptica curvature. The single annular turn 10"th us formed comprises the end portions 14 and 15 and' as a result of the severing operation I usually find that there .is a burr 16 upon one or both of the ends 14 or 15.

. if desired, the rings may be fed automati-.

. the ends of the ring to a While the ideal result of bending and severing would provide a'turn 10 whose ends 14 and 15 would be directly opposite to each.

other, I find in practice that, as shown .at the upper part. of Fig. 5, the ends 14 and 15 of the ring 10? are not always directly 0 posite, one end being at a greater radial istance from the center of the ring than the other. Also as illustrated at the lower part of Fig. 5 I sometimes find that burrs 16are roduced in the cutting operation atthe ra ial faces of the ring,

According tothepresent process the next desirable step is to remove the burrs 16 or 16" from the ends of the rin and this may be accomplished as shown in ig.; by applying n 1n This operation may be per. ormed y hand or,

, cally to a machine for removingthe burrs either by grinding, milling or otherwise.

Further possibleresults of .the bending operation are indicated in Figs. 7 and 8. As

' form, as shownin :with the present process, my next step has for wheel 17 indicated. in Fig. 7 the corners 19 of the'ring after bending are sometimes rounded and, as

shown in greatly exaggerated formin Fig. 8, the. bending of. the material,particular1y if material originally of rectangular cross sec- .tion is employed, may result'in the production of a ring 20 whose outer surface 2? is less'in width than its inner surface 3*. Other slight irregularities may also be produced in bending or may result from slight initial irregularities in thickness of the wire produced in the d'rawng or rolling operation. Furthermore, as indicated in Fig. 11, if the bending of the wire be accomplished by a coiling oper ation, the annular turn, aftersevering from the original length of wire, may have a slightly helical form so. that the ends 15 and 16 do not lie exactly opposite to each other.

For curing such defects as indicated in Figs. 7 and 8 or others of generally like character, I prefer next tosubject the ring to pressure applied to its radial faces. -As indicated in Fig. 9, the ring lOis supported upon the upper surface 21 of the lower platen of a press while the upper platen 22 of the press rests upon the upper radial face of the ring. The platens of the press will for this purpose be accurately smooth and parallel and the press should be capable of exerting a heavy pressure, for exampleof the order of twentyfive tons, so as substantially to flatten the radial faces of the ring and reduce the ring to substantially rectangular cross section, as indicated in Fig. 10. v

While the radial faces of the ring, as a consequence of-this flattening operation may be substantially parallel toeach other and nearly flat, the rin may still retain its helical ig. 11, and in accordance its object the removal of this helical formation and the reduction of the ring to true plane form.

I now subject the ring to a heat treatment in which I preferably use instrumentalities such as shown in Figs. 12, 13 and 14. These instrumentalities include a mandrel 23 which may be of cast iron or similar heat resistant material and of a cross section substantlally tical. vI also providev a clamping shell 24 which is preferably of resilient metal and provided with means for drawing it snugly about the rings mounted upon the mandrel.

23. Ifurther' provide a narrow bar 25 which in one dimension is substantially equal to the radial thickness of the ring and in the other dimension is substantially. equal to the width of thegap 13 in the ring. I next mount a series of rings 10 upon the mandrel 23 and arrange them so that their-gaps 13 are in alignment. I then place the bar 25 in'the series of gaps 13 and while subjecting the.

series of rings 10. to endwise pressure suflicient to reduce them to substantlally plane form, I clamp the member 24 about the series of rings with sufiicient firmness to draw them closely about the mandrel and ,to prevent them from moving endwise. I then introduce the mandrel with itsseries of rings into a suitable furnace where they are sub'ected to a temperature of the order of 900 which I find sufiicient to remove all strains intro-- duced by the'bending operation and to 've the rings a permanent set-such that w en cooled theyaccurately retain the shape of the mandrel and have substantially no tendency to return toithe helical form.

Having heat treated the rings I next prodeed to trim the ends 14 and 15 of the ring so as to produce a gap of the desired width and shape. Thus if the'ring is to have a diagonal gap I may, as indicated in Fig. 17 present the ring to a grinding wheel 27 or a milling cutter arranged at the pro er angle and of the proper width so that a slngle passage of the grinding wheel or cutter throu h the gap 13 in the ring will produce the esired width and complemental finished faces 7 28 and 29 (Fig. 18) adapted, when the ends of the ring are brought into contact, to form an overlapping and substantially gas-tight j int.

While these finished end surfaces may be formed by grinding, I contemplate that they also may be produced by a milling o eration, and of course the mlght be-pro uced by filing, although t is latter method would reduces the rin 'next pre er to subject the ringto an operation which accurately flattens its radial faces and to its final axial thickness. I may accomphsh this purpose as indicated in Fig. 22 by placing the ring 10 upon a support 33, for example a magnetic chuck, and subjecting the opposite radial face of the ring to the action of a grinding wheel 33 accurately spaced from the supporting surface of the member 33. In accordance with this process I prefer to grind one radial face of the ring and then to turn the ring over and grind the opposite face, the last grinding resulting in the reduction of the ring to the final desired thickness.

Instead of grinding the radialfaces of the ring as just described, I may produce similar well as at. the earlier stage which I have described with reference to Fig. 10, I intend to include both gradual pressure and also suddenly applied pressure, that is to say, pressure in the form of a blow, and in most instances I prefer to' supply the ressure suddenly in the form of a blow since I'found ..that pressure thus'applied is far more eflicacious "than is more slowly and gradually aplpIlied pressure. p v

aving thus reduced the ring toits' final axial thlckness and provided accurately smooth and parallel radial faces, I next if hardly be a commerciaLmethod of perforinnecessar finish the outer peripheral surface in this step. I

nstead of. making a diagonal gap as indicated in Figs. 17, 18- and 19, I may rovide a step-end formation as shown in ig. 20 where the ends 14 and 15 of .the ring are provided with'overlappin surfaces 28 and sometimes produced, although I contemplate that methods of trimming the ring may be devised which will not result in the production. of such burrs.- If such burrs be produced I. propose as the next stepin the present procif desired, subject the rings to inspection and Jess to remove these burrs and this may be accomplished as indicated inFig. 21 by subjecting the ring to the action of a grinding wheel 32. Of course, these burrs might be removed by a milling operation orby filling eral surface of each ringindividually, I prefer, asindicated in Figs. 24 and 25, to mount a large number of rings upon a mandrel 36 preferably staggering the aps 13 of the several rings. I then 'preferab y mountthe mandrel 36' upon centers, so thatit may be rotated at desired speed, and while rotating the mandrel 36 I bring a grinding wheel 37 into engagemnt with the peri heral surfaces of the rings, causing'the grin ing wheel or mandrel or both to move axially so as to grind the entire series of rings and reduce them to the proper outside diameter.

. After this final grinding operation I may,

. measurement, rejecting all rings which do not conform to the.desired-qualifications.

As previously stated, the several steps above described result in the production of a ring and durability, and in case, simplicity and low cost of ,production, while at the same time the ring possesses none of the disadvantages which have previously prevented steel rings fromcoming into commercial'use.

While Thavespecifically described certain steps as desirable in-the present process, I contemplate, as above suggested, that some of these steps may be omitted and that other or possibly equivalent steps may be substituted. for those here described and that under some circumstances additional steps may be.

necessary to produce rings having peculiar and unusualcharacteristics, but I wish it .to

rings from hard steel-wire or rod which comprises as steps bending alength of wire or rod, whose surface at least is sufliciently hard to form a good bearing against a cylinder wall, to form a single annular turn, severing said turn from the material before completing a subsequent turn, atjsuch' a point'a's to form a ring having a gap therein, and remov- 2. Thatmethod of making rings which comprises as steps temperature such as ing any burr produced in severing the material. p split packing rings which. comprises as steps bending a length of steel rodor wire of from 0.6% to 0.8% carbon to form a single annular turn, severing said turn from the-length to form a ring having a gap at onepoint, flattening the radial faces of the ring, and removing burr.

produced in preceding steps.

rings which comprises as steps bending the end portion ofa length of steel wire or rod of at least 0.5% carbon'to form ahelical turn,

severing said turn from the length ofvwire at such a point as to providea ring having a gap therein, compressing the ring axially to reduce it to the form of aplane ring, and heating the ring while'so axially compressed to impart a permanent set thereto.

4. That method of making acking n g the end portion. of a length of steel wire or rod of at least'0.5% carbonto form a helical turn, severing said turn from the length of wire at such a point as to provide a havinga gap therein, confining said ring both axially and circumferentiallypredetermined bounds, andheating the ring so confined to a to impart a permanent set thereto. b

5. That method of making split packing rm hich comprises as. steps bending a I length of wire havin substantially the physical characteristics -0 steel of approximately 0.6% carbon to form a single annular-turn,

severing said turn from the length to provide a ring aving a gap at one point, clamping said ring about a forming mandrel of predetermined contour, and heating the ring while clamped to the mandrel to a temperature of approximately 900 F.

- 6. That method of making split packing rings which comprises as steps bendingthe end portion of a length of steel Wire or rod of at least 0.5% carbonto form a helical turn, severing said turn from the length of wire at such a point as to provide a ring having a gap therein, placing said ring together with likerings upon a mandrel, compressing the several rings axially, confining the rings circumferentially to make then conform to the mandrel, and heating the mandrel and rings to substantially 900 F.

7. That method of making split packing rings which comprises as steps bending a length of metallic rod or wire to form an annular turn, cutting off said turn from-the length at such a point as. to produce a ring having a gap therein flattening the radial faces of the ring, condning the ring circum- 1 ferentially within predetermined bounds, and 3. That method of making split-packing- 9. That method of making split packing rings which comprises assteps bending a length atsuch a point as to produce a ring tour, clampingthe entire length of the turn length of metallic rod'orwire to form an annular turn, cutting off said turn from the.

having a ap therein, flattening the radial faces of t e ring, confining the ring-both axially and circumferentially within predetermined bounds, and heating the ring; to a temperature such as to cause it to acquire a permanent set.'

10. That method of making split packing rings which comprises asste'ps' bending a length of hard steel rod or wire in such a way as toform a single annular turn mibstan- ,tially devoid of permanent helical set, out-- tingiofi said turn from the length at such a int as to produce a rin having a gap there- 1n, and fimshin the en posite sides of t e complemental surfaces. I

11. That method'of making spl1t packing i "which comprises as steps bending a length of hard steel rod or wire in such a Way of the mug at opgap to provide accurately v .faces adapted to contact with each other'to form atight joint. I

12. That method of making split packing rings which comprises as steps bending I a length of hard steel rod or wire in such a way as to form a single annular turnsubstantially devoid of permanent helical set, cutting oflf said .turn from the length at such a point as to produce a ring having a gap there n, subjecting said ring, while confined within predetermined bounds, to a temperature such as to impart a permanent set thereto, and shaping the end portions of the ring at opposite sides of the gap to form accurately complemental surfaces.

13. That method of making split packing rings which comprises as steps bending a length of hard steel rod or wire so as to form an elliptical turnsubstantiall devoid of permanent helical set cutting 0 said turn from the len h at "such a point as to produce a ring having a gap therein adjacent to one end of its minor'axis, heating the ring to a temperature such as substantially to remove internal strains set up in the prior steps, removing material at the ends of the ring at opposite sides of the gap to produce complemental end surfaces, and removing burrs produced in the last=named step,

14. That metlfod of'making piston rings which comprises as steps bending a length of steel Wire to form'an annular turn, cutting off said turd from the length at such a point as to produce a ring having a gap thereilnheat treating the ring while confining it axially and circum'ferentially within predetermined bounds, and'flattening its radial faces."

15. That method of making piston rings which comprises as steps bending a length of steel wire to form an annular turn, cuttingofl' said turn" from the length at-such a point as to produce a ring having a gap therein,

.,flattening the radial faces of the ring, confinit to a temperature of-the order of 900 F and again flattening the radial faces ofthe.

.ing the ring axially and circumferentially within predetermined bounds and subjecting ring. 7 n

' 16. That method of making piston rings which comprises as steps bending a length of steel wire .to fox-man annular turn, cutting ofi'rsaid turn from the length at such a point as to roduce'a ring having a. gap therein,

flattening the radial faces-of the-ring, removmg burrs produced in prior steps, confining the ring clrcumferentially and subjecting it to heat suflicient to impart a permanent set site sides of tlie gap, removing burr produced in the trimming operation, and'again and.

accurately flattening theradial faces of the 17 That method of making piston rings which comprises as steps bendinga length of steel wire to form an annular turn, cutting ofi said turn from the length at such'a point as to roduce a ring having a gap therein, flattemng the radial faces of the ring, removing burrs produced in prior steps, confining the ring-circumferentially and subjecting it to heat sufficient to impart a permanent set to it, trimming the ends of the ring at opposite sides of the gap, and grinding the radial faces of the ring.

18. That process of making split packing rings which comprises as steps bending a length of metallic rod or wire to form an annular turn, cutting oif said turn from the length at such a point as to produce a ring having a gap therein, confining and heat treating the ring upon a forming mandrel to impart the desired contour to the ring, trimming the ends of the ring at the gap to provide compleniental surfaces, and grinding the peripheral surface of the ring.

19. That process of making split packing rings which comprises as steps bending alength of metallic rod or wire to form an annular turn, cutting off said turn from the length, at such a point as to produce a ring having a gap therein, grinding the. radial faces of the ring, and grinding the peripheral surface of the ring.

20. That method of making piston rings which comprises as steps bending a length of steel wire to form an annular turn, cutting ofi saidturn from the length atsuch a point as to produce a ring having a gap therein,

flattenmg the radial faces of the ring, remov-v ing-btfrrs produced in prior-steps, confining the ring circumferentially and subjecting it to heat sufiicient to impart a permanent set to it, trimming the ends of the ring at opposite sides of the gap, removing burr formed in the trimming operation, grinding the radial faces of the ring, and grinding the peripheral surfaces of the ring. 21..That method of making'piston rings fromsteel wire or rod which comprises as steps bending the wire toform a turn of substantially elliptical contour, cutting off said turn from the wire at such a-point as to provide a substantially elliptical ring having a gap adjacent to one on of its shorter axis, placing the ring upon a' mandrel of substan tially elliptical contour, compressing. and f heating the rin to conform it to the mandrel, and finishing the radial and faces of the ring. i Y

22. That method of making piston rings from steel wire. or rod which comprises as steps bending the wire to form a turn of subperipheral sur- 1 stantially elliptical contour, cutting off said 7 gap adjacent to one en of its shorter axis,

placing the ring upon a mandrel of substantially elliptical contour, compressing and heating the ring to conform it to the mandrel,

' trimming the end portions of the ring to prowhich comprises as steps bendin vide complemental surfaces at opposite sides of the gap, grinding the-radial faces of the ring, and grinding the peripheral surfaces of the ring.-

23.: That method of making piston rings which comprises as steps bending a length of steel wire to form an annular turn, cutting ofi' said turn from the length at such a point as to produce a'ring having a gap therein, flattening the radial faces of the ring, removing burrs produced in prior steps, confinin the ring circumferentially and subjecting 113 to heat sufiicient to impart a permanent set to it, trimming the ends of the ring at opposite sidesvof the gap, assembling the ring with others upon a mandrel, and moving the mandrel relatively to a grinding wheel whereby to grind the peripheral surfaces of the several rings.

24. That method of making piston rings a length of steel rod or wire to produce armg having a gap therein, flattening the radial faces of the ring, confining the ring circumferentially and subjecting it to heat suflicient to impart a permanentset to it,trimming the ends of the ring at opposite sides of the gap, grinding the radial faces of the ring and grinding the peripheral surfaces of the ring. a

25. That method of making piston rings. which comprises as steps bending a length of steel rod or wire to produce a ring having a gap therein, flattening the radial faces of the ring, confining the ring circumferentially and subjecting it to heat suflicient' to impart a permanent set to it, trimming'the ends of i the ring at opposite sides of the gap, as-

sembling the ring with others upon a mandrel and moving the mandrel relatively to a grinding wheel whereby to grind the peripheral surfaces of the several rings.

26. That method of making piston rings from a length of steel wireor rod which comprises as steps bending the wire to form a ring of substantially elliptical contourhaving a gap adjacent to one end of its shorter axis,

placing the ring .upon amandrel of substantially elliptical contour, compressing and heating the ring to conform it to the mandrel,

trimming the end portions of the, ring to .provide. complemental surfaces at opposite sides of the gap, grinding the radial faces of the ring and grinding. the peripheral surface of the ring.

27 That method of making piston rings which comprises as. steps bending a length of metallic rod or wire to form asingle an- 28. That method of making piston rings which comprises as steps bending a length of m'etallicrod or wire'to'form a single annular turn, severing said turn in such a way as'to form a' ring having a gap therein, and simultaneously finishing the ends of the ring at opposite sides of the gap to produce finished complemental end faces adapted to contact with each other to form a tight joint. Signed by me at Boston,Massaohusetts, this 24th day of May, 1927.

LEWIS C. 'MARSHALL. 

